494 HISTOLOGY 



specimen is passed from absolute to a mixture of equal parts of absolute 

 and chloroform for 2 to 6 hours, and then to pure chloroform for an equal 

 length of time. It is then transferred to a saturated solution of paraffin in 

 chloroform, kept warm by placing on top of the paraffin bath, for 2 to 4 

 hours, and is then put into melted filtered paraffin. 



The melting point of the paraffin used varies with the temperature in 

 which it is to be cut. During the winter, paraffin melting at 5o-52 C. 

 should be used, while during the summer paraffin with a melting point of 

 56-58 is best. Harder paraffin is required for thin than for t&ck sec- 

 tions. The melted paraffin should be kept in a paraffin bath or thermostat 

 maintained at a temperature but slightly higher than the melting point of 

 the paraffin. 



The specimen should be left in the melted paraffin for the shortest time 

 which will allow thorough infiltration, as heat is very injurious to the tissue. 

 For average specimens, 3 hours is sufficient. Transfer to fresh paraffin 

 at the end of i^ or 2 hours. At the end of the full time, the specimen is 

 to be imbedded. 



The imbedding frame consists of a glass plate and two L-shaped pieces 

 of metal. By sliding the latter back and forth on one another, the size 

 of the enclosed space or box may be varied. Before using the frame, 

 the inner surfaces of the metal pieces and that part of the glass plate on 

 which they rest are rubbed with glycerin. It should form a thin film 

 over the surfaces, but not accumulate in drops. Melted paraffin is 

 poured into the box and the specimen is transferred to it with a spatula. 

 The specimen sinks to the bottom, and may be arranged in any desired 

 position by means of needles warm enough to prevent the paraffin solidify- 

 ing over their surfaces. The paraffin must be quickly cooled by lowering 

 the frame into a basin of cold water so that the water comes up on the 

 sides of the metal pieces. As soon as a resistant film has formed over 

 the surface of the paraffin, the entire frame may be submerged, and in 

 a few minutes the glass plate and metal pieces may be detached from the 

 solid paraffin. The block may be sectioned as soon as it is thoroughly 

 cooled. 



When a number of specimens are to be imbedded, a flat dish of suitable 

 size may be used. After a thin layer of glycerin has been coated over 

 the interior, the dish is filled with a sufficient quantity of melted paraffin 

 and the blocks are put into position. The mass is cooled and removed 

 as before, and the large mass is cut into smaller parts, each containing a 

 specimen. 



One or several specimens may be imbedded in paper boxes of suitable 

 size. The tabs at the ends may be labelled and the specimens kept in 

 the boxes until wanted; otherwise labels may be scratched in the paraffin 

 with needles. 



